sparse: directly inline the `set_tracked` and `copy` wrapping core is already aware of sparse, so lets move the handful of line of code that deal with this for the sake of simplicity and explicitness.

spares: clarify some test about merging copies This new output clarify the important part out this merging : we want to be able to record the copy source even it is outside of the sparse profile.

sparse: drop the useless wrapping of `dirstate.set_untracked` The code of the wrapper only act in the case where the file is not tracked, so this has not effect for `untracked`. In addition the message explicitly mention `add` of a file and no test are breaking if we drop this. So we drop this for simplicity and cleanup

sparse: directly inline the `rebuild` wrapping Core is already aware of sparse, so lets move the handful of line of code that deal with it in `dirstate.rebuild` for the sake of simplicity.